Wireless networks are used by consumers, businesses, service organizations (among others) to establish or extend local area networks to locations that are not readily or desirably connected to wire network interface cards.
Networks may be operated so as to restrict access to authorized users. Alternatively, a wireless network may be open to access to anyone, either for a fee or without charge. For example, open networks or “hot spots” are often operated by retail establishments, transportation hubs, medical facilities, and educational institutions to permit access to the Internet to users of wireless stations, such as laptops, smartphones, and tablets, through a base station or access point (AP).
A wireless network typically communicates using a protocol that defines message structures (sometimes referred to herein as “frames”). A message frame may include a field for a network identifier or name, the media access controller address (MAC) of the station from which the frame is broadcast, and other information. In order to connect to a network, a wireless station must first find a compatible network that is within range of its transceiver. This process is typically accomplished through either passive or active scanning. In passive scanning, an AP broadcasts its network name and other information in a message frame. In active scanning, the wireless station requests a response from an access point by broadcasting the network ID of the network it is seeking to join. Alternatively, an active scanning process may include broadcasting a request for a response from any network within range of the wireless station. The APs that are within range broadcast their SSIDs to the wireless station. The wireless station may select a wireless AP to associate with from the list of responders.
Another architecture allows wireless stations to announce their presence to other wireless stations and to form networks in which there is no AP. In this case, the wireless station seeking other wireless stations broadcasts its network identifier and receives a response from other wireless stations within range.
Once a compatible network is found, the wireless station establishes a connection to a wireless network through an exchange of messages that authenticates the wireless station to an access point (or a wireless station when there is no AP present) and then associates the wireless station with that access point or wireless station. By way of illustration and not by way of limitation, an IEEE 802.11 network (or more commonly, “Wi-Fi” network) provides communications between a Wi-Fi AP and Wi-Fi enabled device. The Wi-Fi AP transmits the network name in the form of a service set identifier (SSID). The SSID is typically a 1 to 32 byte value that segments the airwaves for usage. If two wireless networks are physically close, the SSIDs label the respective networks, and allow the components of one network to ignore those of the other. The SSID is present in beacon messages sent by an AP, a probe request sent by a wireless station, probe responses sent by an AP, an association request sent by a probe request sent by a wireless station, and a re-association request sent by a wireless station. When wireless stations are operated without an access device (IBSS or ad-hoc mode), probe requests from one wireless station may be answered by another wireless station with a probe response.
A beacon message is sent by an AP 5 to 20 times per second. The beacon typically includes the SSID, the time, capabilities, supported data rates, and physical layer parameter sets that regulate the smooth operation of a wireless network.
The information that is broadcast by an AP may be received freely by any device that operates a compatible receiver. Unless the device intends to connect to the network supported by the AP, the information that is broadcast by the AP is simply ignored.